In prelaunch preparation of a spacecraft, the filling of the fuel tanks for a rocket engine of the spacecraft presents environmental conditions within the spacecraft that are monitored and adjusted prior to launch. The fuel components for the rocket engines are typically filled into separate tanks within the spacecraft in a liquid state. In a liquid state these fuel components are kept at an extremely low temperature. As a result, the filling of the fuel tanks within the confines of the spacecraft provide a cooling effect to the ambient volume surrounding the tanks which hold these liquid fuel components.
In the instance of liquid oxygen, at one atmosphere, its temperature can be approximately minus two hundred and ninety three degrees Fahrenheit (−293° F.) (−180.5° C.). In the instance of liquid hydrogen, at one atmosphere, its temperature can be approximately minus four hundred and twenty three degrees Fahrenheit (−423° F.) (−253° C.). With the fuel tanks holding these liquid fuel components, the surrounding ambient volume temperature within the confines of the spacecraft can reach temperatures of approximately minus forty degrees below zero Fahrenheit (−40° F.) (−40° C.). This temperature within the enclosed volume of the spacecraft can affect the performance of avionic equipment and mechanical equipment positioned in the vicinity of the fuel tanks. For example, lithium ion batteries to optimally function should be maintained at a temperature of at least plus forty degrees Fahrenheit (+40° F.) (4.44° C.). Similarly, such temperatures could also affect the performance of mechanical equipment such as valves, positioned within the vicinity of the fuel tanks. In current efforts to control the temperature proximate to the equipment located within the enclosed volume, conditioned purge gas is released from the distribution duct into the enclosed volume, raising the temperature within the entire closed volume. As result, energy is consumed to elevate the temperature in the vicinity of the avionic and mechanical equipment prior to launch.
Additionally, the fueling process can cause fumes from the liquid fuel components to enter the enclosed volume within the spacecraft. These fumes can flow within the enclosed volume to be in proximity to avionic and mechanical equipment and are preferably removed prior to launch.
In an attempt to raise the temperature and adjust the fuel fume content within the enclosed volume within the spacecraft prior to launch, purge gas such as nitrogen gas has been used to purge the enclosed volume of the spacecraft of the fuel fumes. The nitrogen gas is introduced at a temperature of approximately plus sixty degrees Fahrenheit (+60° F.) (15.55° C.) in an attempt to counter the cooling effect of the temperature within the enclosed volume caused by the low temperature liquid fuel components contained within the fuel tanks. The purge gas originates from a duct carrying the pressurized purge gas and is released into the enclosed volume within the spacecraft. With the introduction of the purge gas into the enclosed volume, the fumes can be purged, however, this higher temperature of the purge gas also contacts the fuel component tanks.
To carry larger payloads into space, larger rocket engines will be used that will have larger fuel tanks. As fuel tanks for spacecraft are designed to be larger, obtaining a uniform desired temperature of the atmosphere within the enclosed volume within the spacecraft can be more difficult than in smaller spacecraft with smaller fuel tanks and smaller enclosed volumes. As a result, warming the avionic equipment and mechanical equipment to a desired operational temperature will become more difficult to attain without introducing larger volumes of conditioned nitrogen gas, for example, into the enclosed volume of the spacecraft. The nitrogen gas will then, in turn, come into contact with the fuel component tanks and tend to elevate the temperature of these tanks.
As mentioned above, the current method employed is to introduce conditioned purge gas within the enclosed volume of the spacecraft to purge the fumes of the fuel components and to warm the entire bay or enclosed volume of the spacecraft which contains the avionic and/or mechanical equipment. To mitigate the effects of the conditioned purge gas raising the temperature at the fuel tanks, use of traditional duct work to carry the purge to closer proximity to the equipment would be too bulky and would add additional weight to the spacecraft. Introduction of individual heating units for each set up of avionic or mechanical equipment would also add additional weight and complexity to the spacecraft. Moreover, the heater(s) would draw power that could be otherwise used for other functions. Also, contemplating directing a jet stream of conditioned purge air toward the equipment is also problematic. Avionic and mechanical equipment are typically much smaller than a fuel tank, making it difficult to target and direct a jet stream to reach and sufficiently warm the equipment. Additionally, the jet stream of purge dissipates as it travels a distance through an enclosed volume before reaching the target of the avionic or mechanical equipment. As a result, the jet stream approach does not assure sufficient elevation of the temperature of the equipment for optimum operation.